Light modulation system



June16,194z. V, Q HALL ,y 2,286,729

LIGHT MODULATION SYSTEM K FledFeb. l5, 1941 SOURCE VINCENT E.HALL Y Y INVENTOR j K TTORNEYS Y Patented une' 16,.v Y 1942 s "l PATENT LIGHT MoDULATIoN srs-TEMY t Vincent CfHall, Rochester, N. Y., ass'gnor to Eastman' Kodak Company, Rochester', N. Y., 'a corporation/of New Jersey Application February 13,1941, Serial No. 378,781 v f This 4invention relates to a light modulating systemand particularly-to a system for recording signal currents on a photographic medium Where' byV the modulation range is greatly. extended.

In any system for modulating a light beam and especially in producing a photographic image," such as in sound recording or the electrical transmission of pictures, :the limited rangeof light f intensities over which the light modulating-system will operatesatisfactorily is arserious factor. Thus, a glow Alamp can be dependtwo light valves I6 and output circuits Miami I9, respectively, Vof two ampliers, the input circuits of which are con- .such asa microphone 20.. 1

Thesignal from the microphone 20 is applied 'l across `two potentiometers 2| and 22 which con# trol thev voltage applied to the grids of tubes 23 and 24, respectively, of the ampliers having the ed on for a range of light intensitiesof not over ,I

60-1, while-a light valve carefully adjusted may go toa range of 100A-1, or even-2004. but avalvef is not usuallyconsistent inits operation over such ranges.

The present invention which extends the range.

of modulation very materially makes use of two modulating systems, such as a"glow lampand light valve, or two light valves with a constant source, in series and so arranged that they operate over different selected intensityvranges of the currents controlling the modulation.

With the light modulating system according to the invention it is possible to obtain a range l of light intensities as high as 40,000 to 1 so that by limiting the range of the valves to one over which they operate very satisfactorily, ranges outputsl andflS. The tube 23 is connected to n arefcnnected to the Y nected to a common source of modulated currents the light valve 'I6'` through a power amplier tube f25, a coupling transformer 26, al rectier 21 the outplltvoircllt I8. The rectier '21 i maybe made'linear by a suitable resistance 28.

The tube 2,4A is similarly .connected to 'the' light valve Il through a power tube 29, a coupling transformer 30,` af rectifier 3l andthe output of 1000-1 to 2000-1 can be obtained. This range is ample for sound recording and is sufficient for making color separation records from subtractive color pictures and the like.

In accordance with the invention, two light modulating devices are arranged serially in a light beam and one device is operated to' capacity before the other device is called into action. In other words, the complete range of amplitudes of the modulating currentsv is divided into two ranges, one ofy which actuates exclusively one of the modulating devices, and the other range of which actuates exclusively the other of the modulating devices.

The invention will be fully understood from the following description when read in connection with the accompanying u, drawing and its scope will be pointed out in the appended claims.

In the drawing, Fig. 1 is a diagram illustrating vgraphic lmf'll -is'dened by lenses l2, I3, I4

and I5 and two ylight valves I6 and I1.. These the preferred form of the invention applied to circuit I9.v A resistance 32 is used to make linear the rectier 3|.

A source of potential 33 serves to bias the grid of tube 23 to a value such that the grid goes positive at a voltagewhich will give suflicient signal to open completely the light valve I6.- A resistor 34 is used to limit the positive voltages applied to the grid oftube 23.

A sourceof potential 35 for biasing the grid of the tube 24 is correlated to the adJustment of potentiometer 22 so that, for all signals less than those whichwill completely open the light valve I6, the grid of tube 24 is sufliciently negative to prevent the :flow of plate current and therefore the light ,valve I1 is not energized.

However, when the signal potential is higir is enough to render the'tube 24 conducting andV all signal currents in the range above this value are impressed on the light valve I1. Since the cut-offs of the two ampliers will probably be not exactly sharp, they should be'adjusted to give the desired shape of reproduction curve which should be sulrstantially'l straight'v over most of the range.

The simplified form of a suitableoptical sys-V tem for use with they present invention shown conventionally in 2 is convenient for using two valves spaced serially in the light beam andl u operated in accordance with the invention.

It is to be understood that the invention is not tions will readily suggest themselv skilled vin the art. Other ampllers and otherA forms' of light modulating devices may beem ployed for practicing the invention, the scope of which is pointed out in the appended claims.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a sound recording system, means for translating sound modulated current into light values comprising a first light beam modulator supplied with sound modulatedcurrent, and a second light beam modulator supplied with modulated current only when'thedntensltyoi' such current exceeds a predetermined value.

2. In a sound recording system, a pair of spaced iight valves, means denning a'beamj of4 light which passes serially through the two light valves, an electrical network adapted when supsity for changes in intensity, within a predetermined diiierent range.

5. In a system for recording modulated currents on a photographic medium, a light modulating means, means for varying the light falling on said light modulating means in accordance with the modulated currents throughout one range of amplitudes, and means .or actuating said light modulating means in accordance with the modulated currents only throughout another range of amplitudes. o

6. In a light beam modulator, the combination of two light valves spaced serially in the light beam', vand an' electric circuit for actuating said plied with sound modulated current to. apply. to

one of said valves substantially all of such current less than a predetermined intensity and to apply to the other of said valves all of such c'urrent in excess `of said predetermined intensity.

3, In a system a photographic medium, a pair ot modulators for l,light valves in accordance with electric impulses suppliedto the circuit, said 'circuit being so arranged that` one of the light valves is actuated only by the portions of such impulses which lie above a predetermined intensity level.

-20 for recording signal currents'on l the same light beam, an electric circuit for sepf arating the signal currents into two intensity i ranges and for applying the `currents in one intensity clusively, the. currents in the other intensity range being applied exclusively tothe other light modulator. 1 f

4. InV a systemior recording signal currents on a photographic medium, rthe combination of a pair of modulators I'iositloned` in'a light beam. an

A electric circuit adapted to' be `energized by signal:V

currents for controlling one `of'said modulators in accordance 'with signal currentrinten'sity for changes in intensity `within a predetermined 'f range, and for controlling the other of said mod-Y ulators in accordance with signal currentintenrange to one of the light modulators ex- 7. lAy sound recording system comprising a source of alternating currents to be recorded, a light beam, a first means for directly modulating said beam with a certain range of amplitudes of said alternatingV currents, and a second means for directly modulating said beam with another range of amplitudes of said alternating currents.

48. Afcircuit comprising a source oi alternating currents, two ampliners having a common input circuit connected to the source of alternating currents, a pair of output circuits for said amplifiers, a light valve connected to each output circuit, one of said amplifiers having an initial bias different from the other of said amplifiers so that one of said ampliiiers supplies currents to its 'associated' light valve only overl a predetermined range oi amplitudes of said alternating currents.

r VINCENT C. HALL. 

